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BIER BFD
draft-ietf-bier-bfd-07

Document Type Active Internet-Draft (bier WG)
Authors Quan Xiong , Greg Mirsky , fangwei hu , Chang Liu , Gyan Mishra
Last updated 2024-07-26
Replaces draft-hu-bier-bfd
RFC stream Internet Engineering Task Force (IETF)
Intended RFC status (None)
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Stream WG state In WG Last Call
Document shepherd Donald E. Eastlake 3rd
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Send notices to d3e3e3@gmail.com
draft-ietf-bier-bfd-07
BIER WG                                                         Q. Xiong
Internet-Draft                                           ZTE Corporation
Intended status: Standards Track                               G. Mirsky
Expires: 27 January 2025                                        Ericsson
                                                                   F. Hu
                                                              Individual
                                                                  C. Liu
                                                            China Unicom
                                                               G. Mishra
                                                            Verizon Inc.
                                                            26 July 2024

                                BIER BFD
                         draft-ietf-bier-bfd-07

Abstract

   Point to multipoint (P2MP) BFD is designed to verify multipoint
   connectivity.  This document specifies the application of P2MP BFD in
   BIER network.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 27 January 2025.

Copyright Notice

   Copyright (c) 2024 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights

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   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions used in this document . . . . . . . . . . . . . .   3
     2.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
     2.2.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   3.  BIER BFD Encapsulation  . . . . . . . . . . . . . . . . . . .   3
   4.  BIER BFD Session Bootstrapping  . . . . . . . . . . . . . . .   3
     4.1.  Bootstrapping a BIER BFD Session Using BIER Ping  . . . .   4
     4.2.  BGP Bootstrapping . . . . . . . . . . . . . . . . . . . .   4
   5.  Discriminators and Packet Demultiplexing  . . . . . . . . . .   5
   6.  Active Tail in BIER BFD . . . . . . . . . . . . . . . . . . .   5
     6.1.  Unsolicited Head Notification Mode  . . . . . . . . . . .   5
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
     9.1.  BIER OAM Message Type . . . . . . . . . . . . . . . . . .   6
     9.2.  BFD Discriminator TLV . . . . . . . . . . . . . . . . . .   7
     9.3.  BGP's BFD Discriminator Attribute Mode of P2MP Session with
           Active Tails  . . . . . . . . . . . . . . . . . . . . . .   7
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   Bit Index Explicit Replication (BIER) [RFC8279] provides the
   forwarding of multicast data packets through a multicast domain.  It
   does so without requiring any explicit tree-building protocol and
   without requiring intermediate nodes to maintain any per-flow state.

   [RFC8562] defines a method of using Bidirectional Forwarding
   Detection (BFD) to monitor and detect failures between the sender
   (head) and one or more receivers (tails) in multipoint or multicast
   networks.  [RFC8563] describes active tail extensions to the BFD
   protocol for multipoint networks.

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   This document describes the procedures for using such mode of BFD
   protocol to monitor connectivity between a multipoint sender, Bit-
   Forwarding Ingress Router (BFIR), and a set of one or more multipoint
   receivers, Bit-Forwarding Egress Routers (BFERs).  The BIER BFD only
   supports the unidirectional multicast.  This document defines the use
   of P2MP BFD as per [RFC8562], and active tail as per [RFC8563] for
   BIER-specific domain.

2.  Conventions used in this document

2.1.  Terminology

   This document uses the acronyms defined in [RFC8279] along with the
   following:

   BFD: Bidirectional Forwarding Detection.

   OAM: Operations, Administration, and Maintenance.

   P2MP: Point to Multi-Point.

2.2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  BIER BFD Encapsulation

   BIER BFD encapsulation uses the BIER OAM packet format defined in
   [I-D.ietf-bier-ping].  The value of the Message Type field MUST be
   set to BIER BFD (TBD1 will be assigned by IANA Section 9.1).  BFD
   Control packet, defined in Section 4 [RFC5880], immediately follows
   the BIER OAM header.  The operation of Multipoint BFD with the BFD
   Control Packet is described in [RFC8562].

4.  BIER BFD Session Bootstrapping

   As defined in [RFC8562], a BIER BFD session MAY be established to
   monitor the state of the multipoint path.  The BIER BFD session could
   be created for each multipoint path and the set of BFERs over which
   the BFIR is requested to run BIER BFD.  The BFIR, according to
   Section 5.7 of [RFC8562], MAY bootstrap the BFD session using a BIER
   OAM message (Section 4.1) or the control plane (Section 4.2).  Either
   method MUST refer to the root of the multipoint path and the value of
   My Discriminator associated with the path to the set of BFERs.  The

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   BIER BFD bootstrapping MUST be repeated when the value of My
   Discriminator is changed.

4.1.  Bootstrapping a BIER BFD Session Using BIER Ping

   The BIER OAM could be used for bootstrapping the BIER BFD session.
   The BFIR sends the BIER OAM Echo request message carrying a BFD
   discriminator TLV which immediately follows the Target SI-Bitstring
   TLV (Section 3.3.2 of [I-D.ietf-bier-ping]).

   The Target SI-Bitstring TLV MUST be used to carry the set of BFER
   information (including Sub-domain-id, Set ID, BS Len, Bitstring) for
   the purpose of the session establishment.

   Figure 1 displays the format of BFD Discriminator TLV.

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |         Type = TBD2           |             Length            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                        My Discriminator                       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      Figure 1: BFD Discriminator TLV

   where:

   *  Type indicates BFD Discriminator TLV.  The value (TBD2) is to be
      allocated by IANA (Section 9.2).

   *  Length MUST be set to 4.

   *  My Discriminator - four-octet long field.  The value is the local
      discriminator generated by BFIR for this session.  This
      discriminator MUST be used as the My Discriminator field in the
      BIER BFD Control packets sent by the BFIR.

4.2.  BGP Bootstrapping

   [RFC9026] describes the applicability of [RFC8562] in the detection
   of a Multicast Virtual Private Network.  The new BGP Attribute, BFD
   Discriminator, can be used to bootstrap a p2mp BFD session according
   to [RFC8562].  To bootstrap a p2mp BFD session with active tails
   according to [RFC8563] IANA is requested to allocate a new value
   (TBD5) for the BFD Mode (Section 9.3).

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5.  Discriminators and Packet Demultiplexing

   As defined in [RFC8562], the BFIR sends BFD Control packets to the
   set of BFERs over the multipoint path via the BIER BFD session with
   My Discriminator is set to the value assigned by the BFIR, and the
   value of the Your Discriminator is set to zero.  The set of BFERs
   MUST demultiplex BFD packets based on a combination of the source
   address, My Discriminator value.  The source address is BFIR-id and
   BIER MPLS Label (MPLS network) or BFIR-id and BIFT-id (Non-MPLS
   network) for BIER BFD.  My Discriminator value is advertised in BIER
   BFD bootstrapping using one of the options described in Section 4.

6.  Active Tail in BIER BFD

   [RFC8563] defined an extension for Multipoint BFD, which allows the
   head to discover the state of a multicast distribution tree for any
   sub-set of tails.  For BIER BFD in the active tail mode, the BFIR may
   learn the state and connectivity of the BFERs by allowing the BFERs
   to notify the BFIR.  As per [RFC8563] provides detailed information
   on how the BFIR can use multipoint Poll sequence message or a
   combination of multicast and unicast Poll sequence messages to
   determine the state of the multicast tree.  Also, [RFC8563] describes
   that a BFER can transmit an unsolicited unicast Poll sequence message
   to the BFIR (note that a unicast message must be sent over a path
   which is disjoint from the multicast distribution tree).

6.1.  Unsolicited Head Notification Mode

   [I-D.ietf-mpls-p2mp-bfd] provides detailed information on using the
   unsolicited notification method for P2MP MPLS LSP, which is also
   applicable to BIER.

   In Section 5.2.1 [RFC8563] is noted that "the tail sends unsolicited
   BFD packets in response to the detection of a multipoint path
   failure" but without the specifics on the information in the packet
   and frequency of transmissions.  This document defines the procedure
   of the active tail with unsolicited notifications for BIER as
   specified below.

   Upon detecting the failure, a BFER sends a BFD control packet with
   the following settings:

   *  the Poll (P) bit is set;

   *  the Status (Sta) field is set to Down value;

   *  the Diagnostic (Diag) field is set to Control Detection Time
      Expired value;

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   *  the value of the Your Discriminator field is set to the value the
      BFER has been used to demultiplex that BFD multipoint session;

   *  BFD Control packet is encapsulated in IP/UDP with the destination
      IP address of the BFIR and the UDP destination port number set to
      4784 per [RFC5883]

   *  the BFD Control packets are transmitted at the rate of one per
      second until either the BFER receives valid for this BFD session
      control packet with the Final (F) bit is set from the BFIR or the
      defect condition clears.

   To improve the likelihood of notifying the BFIR of the failure, the
   BFER SHOULD transmit three BFD Control packets defined above in with
   pseudo-random intervals between packets within a one-second interval.

   A BFIR that has received the BFD Control packet, as described above,
   sends the unicast IP/UDP encapsulated BFD control packet with the
   Final (F) bit set to the BFER.

7.  Security Considerations

   For BIER OAM packet processing security considerations, see
   [I-D.ietf-bier-ping].

   For general multipoint BFD security considerations, see [RFC8562].

   A single failure could affect a significant number of BFERs, thus
   causing a spike in the number of BFD Control packets with
   notifications, as defined in Section 6.1.  To mitigate the
   overloading of the control plane, an implementation MUST control the
   number of BFD Control packets passed to the control plane for
   processing.

8.  Acknowledgements

   The authors would like to thank the comments and suggestions from
   Sandy Zhang, Jeffrey (Zhaohui) Zhang, Donald Eastlake 3rd, Reshad
   Rahman, and Les Ginsberg.

9.  IANA Considerations

9.1.  BIER OAM Message Type

   IANA is requested to assign a new type from the BIER OAM Message Type
   registry as follows:

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                 +=======+=============+=================+
                 | Value | Description |    Reference    |
                 +=======+=============+=================+
                 |  TBD1 | BIER BFD    | [this document] |
                 +-------+-------------+-----------------+

                                  Table 1

9.2.  BFD Discriminator TLV

   IANA is requested to assign a new type from the BIER OAM TLV registry
   as follows:

            +=======+=======================+=================+
            | Value | Description           |    Reference    |
            +=======+=======================+=================+
            |  TBD2 | BFD discriminator TLV | [this document] |
            +-------+-----------------------+-----------------+

                                  Table 2

9.3.  BGP's BFD Discriminator Attribute Mode of P2MP Session with Active
      Tails

   IANA is requested to assign a new value from "BFD Mode" subregistry
   (defined in [RFC9026]) in the "Border Gateway Protocol (BGP)
   Parameters" registry according to Table 3:

     +=======+====================================+=================+
     | Value | Description                        |    Reference    |
     +=======+====================================+=================+
     |  TBD5 | P2MP BFD Session with Active Tails | [this document] |
     +-------+------------------------------------+-----------------+

                                 Table 3

10.  References

10.1.  Normative References

   [I-D.ietf-bier-ping]
              Nainar, N. K., Pignataro, C., Chen, M., and G. Mirsky,
              "BIER Ping and Trace", Work in Progress, Internet-Draft,
              draft-ietf-bier-ping-14, 23 July 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-bier-
              ping-14>.

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   [I-D.ietf-mpls-p2mp-bfd]
              Mirsky, G., Mishra, G. S., and D. E. Eastlake, "BFD for
              Multipoint Networks over Point-to-Multi-Point MPLS LSP",
              Work in Progress, Internet-Draft, draft-ietf-mpls-p2mp-
              bfd-07, 2 March 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-mpls-
              p2mp-bfd-07>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC5880]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
              <https://www.rfc-editor.org/info/rfc5880>.

   [RFC5883]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD) for Multihop Paths", RFC 5883, DOI 10.17487/RFC5883,
              June 2010, <https://www.rfc-editor.org/info/rfc5883>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8279]  Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
              Przygienda, T., and S. Aldrin, "Multicast Using Bit Index
              Explicit Replication (BIER)", RFC 8279,
              DOI 10.17487/RFC8279, November 2017,
              <https://www.rfc-editor.org/info/rfc8279>.

   [RFC8562]  Katz, D., Ward, D., Pallagatti, S., Ed., and G. Mirsky,
              Ed., "Bidirectional Forwarding Detection (BFD) for
              Multipoint Networks", RFC 8562, DOI 10.17487/RFC8562,
              April 2019, <https://www.rfc-editor.org/info/rfc8562>.

   [RFC8563]  Katz, D., Ward, D., Pallagatti, S., Ed., and G. Mirsky,
              Ed., "Bidirectional Forwarding Detection (BFD) Multipoint
              Active Tails", RFC 8563, DOI 10.17487/RFC8563, April 2019,
              <https://www.rfc-editor.org/info/rfc8563>.

   [RFC9026]  Morin, T., Ed., Kebler, R., Ed., and G. Mirsky, Ed.,
              "Multicast VPN Fast Upstream Failover", RFC 9026,
              DOI 10.17487/RFC9026, April 2021,
              <https://www.rfc-editor.org/info/rfc9026>.

Authors' Addresses

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   Quan Xiong
   ZTE Corporation
   China
   Email: xiong.quan@zte.com.cn

   Greg Mirsky
   Ericsson
   Email: gregimirsky@gmail.com

   Fangwei Hu
   Individual
   Email: hufwei@gmail.com

   Chang Liu
   China Unicom
   No.9 Shouti Nanlu
   Beijing
   100048
   China
   Phone: +86-010-68799999-7294
   Email: liuc131@chinaunicom.cn

   Gyan Mishra
   Verizon Inc.
   Email: gyan.s.mishra@verizon.com

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